rollup.config.js

import path from "path";
import svelte from "rollup-plugin-svelte";
import resolve from "@rollup/plugin-node-resolve";
import commonjs from "@rollup/plugin-commonjs";
import filesize from "rollup-plugin-filesize";
import livereload from "rollup-plugin-livereload";
import terser from "@rollup/plugin-terser";
import postcss from "rollup-plugin-postcss";
import autoPreprocess from "svelte-preprocess";
import childProcess from "child_process";

const production = !process.env.ROLLUP_WATCH;

export default {
	input: "src/main.js",
	output: {
		sourcemap: true,
		format: "iife",
		name: "app",
		file: "public/build/bundle.js",
	},
	plugins: [
		postcss({
			extract: true,
			// Or with custom file name
			extract: path.resolve("public/build/bundle.css"),
		}),
		svelte({
			preprocess: autoPreprocess(),
			// enable run-time checks when not in production
			dev: !production,
			// we'll extract any component CSS out into
			// a separate file - better for performance
			// css: (css) => {
			//   css.write("public/build/bundle.css");
			// },
		}),

		// If you have external dependencies installed from
		// npm, you'll most likely need these plugins. In
		// some cases you'll need additional configuration -
		// consult the documentation for details:
		// https://github.com/rollup/plugins/tree/master/packages/commonjs
		resolve({
			browser: true,
			dedupe: ["svelte"],
		}),
		commonjs(),

		// In dev mode, call `npm run start` once
		// the bundle has been generated
		!production && serve(),

		// Watch the `public` directory and refresh the
		// browser on changes when not in production
		!production && livereload("public"),
		// If we're building for production (npm run build
		// instead of npm run dev), minify
		production && terser(),
		filesize(),
	],
	watch: {
		clearScreen: false,
	},
};

function serve() {
	let started = false;

	return {
		writeBundle() {
			if (!started) {
				started = true;

				childProcess.spawn("npm", ["run", "start", "--", "--dev"], {
					stdio: ["ignore", "inherit", "inherit"],
					shell: true,
				});
			}
		},
	};
}